Description will be given with reference to FIG. 6 and FIG. 7. FIG. 6 is a configuration drawing of a seat, and FIG. 7 is an exploded perspective view of a seat reclining apparatus for a vehicle of the related art.
As illustrated in FIG. 6, a seat 1 includes a seat cushion 2 configured to support buttocks of a seated person, and a seatback 3 provided so as to be tiltable in the fore-and-aft direction with respect to the seat cushion 2 and configured to support a back of the seated person. Reference numeral 4 denotes a reclining apparatus provided on an axis of rotation of the tilting movement of the seatback 3 and configured to allow/restrict the tilting movement of the seatback 3.
Subsequently, the reclining apparatus 4 will be described with reference to FIG. 7. In the drawing, the reclining apparatus 4 includes a ratchet (first member) 7 formed with inner teeth 7a extending along the circumferential direction of the circle having a center at the center of the relative rotation and having an opened surface on one of the surfaces and a base plate (second member) 5 stacked on the ratchet 7 on the side of the opened surface and provided so as to be capable of rotating relative to the ratchet 7 in the circumferential direction.
The base plate 5 includes four pawls 10 each having outer teeth 10d capable of engaging the inner teeth 7a arranged thereon. The base plate 5 is formed with a guide 5a configured to guide the respective pawls 10 in the radial direction of the relative rotation. Therefore, the respective pawls 10 are capable of moving in the radial direction of the relative rotation.
A rotation cam 9 is configured to move the respective pawls 10 to the locked position where the outer teeth 10d of the respective pawls 10 engage the inner teeth 7a when rotating in one direction about an axis of the relative rotation by pushing surfaces opposite to the surfaces where the outer teeth 10d of the respective pawls 10 are formed.
Three of the four pawls 10 are each formed with a projecting portion 10a. The remaining one pawl is formed with two projecting portions 10b and 10c. The projecting portions 10b and 10c are formed on the side of the outer teeth 10d with respect to the above-described projecting portion 10a. 
A release plate 11 is formed with three cam grooves 11a that allow engagement of the projecting portions 10a formed on the three pawls 10. In addition, a cam groove 11c that allows engagement of the projecting portions 10b and 10c formed on the remaining one pawl 10 is formed. Then, by the rotation of the release plate 11 in the other direction about the axis of the relative rotation, the respective pawls 10 are moved to an unlocked position where the engagement between the outer teeth 10d and the inner teeth 7a is released.
The rotation cam 9 and the release plate 11 rotate integrally by the engagement of three projecting portions 9a formed on the rotation cam 9 with three holes 11b formed on the release plate 11. In other words, when the rotation cam 9 rotates in one direction about the axis of the relative rotation, the respective pawls 10 move to the locked position where the outer teeth 10d engage the inner teeth 7a, and when the rotation cam 9 rotates in the other direction about the axis of the relative rotation, the respective pawls 10 move to the unlocked position where the engagement between the outer teeth 10d and the inner teeth 7a is released.
An operating shaft 12 is connected to the rotation cam 9. On end side of the operating shaft 12 is a prismatic column portion 12a having a rectangular shape in cross section. In contrast, the other end side of the operating shaft 12 includes a circular portion 12b having a circular shape in cross section and an arm portion 12c extending in the radial direction from a peripheral surface of the circular portion 12b. Then, the rotation cam 9 is formed with a hole 9b to which the other end portion side of the operating shaft 12 is fitted at the center of rotation thereof. Therefore, the operating shaft 12, the rotation cam 9, and the release plate 11 rotate integrally.
The respective pawls 10 are urged by a spiral spring 19 locked at one end thereof with the base plate 5 and locked at the other end portion thereof with the prismatic column portion 12a of the operating shaft 12 via the rotation cam 9 so as to be located in the locked position.
Pour projecting portions 7b are formed on a bottom portion of the ratchet 7. An unlock plate 13 is arranged between the release plate 11 and the ratchet 7. The unlock plate 13 is formed with two holes 13a which allow engagement of the projecting portions 7b formed on the ratchet 7, and the unlock plate 13 is restricted from rotating about the axis of the relative rotation. The unlock plate 13 is formed with an arcuate shaped cam holes 13b having a center at the axis of the relative rotation. The cam holes 13b include two wide portions 13c and a narrow portion 13d interposed between the wide portions 13c. The projecting portions 10b and 10c of the pawls 10 engage the cam holes 13b. In a case where the base plate 5 and the ratchet 7 rotate relative to each other and the projecting portions 10b and 10c of the pawls 10 are located in the narrow portion 13d of the cam holes 13b, the pawls 10 having the projecting portions 10b and 10c are configured to be retained in the unlocked position.
An outer peripheral portion of the ratchet 7 and an outer peripheral portion of the base plate 5 are held by a ring-shaped outer peripheral ring 8 and are integrated.
An operation of the reclining apparatus will be described. It is assumed that the ratchet 7 is provided on the seatback side and the base plate 5 is provided on the seat cushion side.
Generally, the respective pawls 10 provided on the base plate 5 are in the locked position where the outer teeth 10d engages the inner teeth 7a of the ratchet 7 by an urging force of the spiral spring 19, and hence the relative rotation between the ratchet 7 and the base plate 5 is restricted, and the seatback 3 is in the state of incapable of rotating with respect to the seat cushion 2 (locked state).
When the operating shaft 12 is operated and the rotation cam 9 is rotated in the other direction against the urging force of the spring 19, the respective pawls 10 move to the unlocked position where the engagement between the outer teeth 10d and the inner teeth 7a is released, and allows the relative rotation between the ratchet 7 and the base plate 5, so that the seatback 3 is allowed to rotate with respect to the seat cushion 2.
When an operating force to the rotation cam 9 is released, the outer teeth 10d of the respective pawls 10 provided on the base plate 5 engage the inner teeth 7a of the ratchet 7 by the urging force of the spring 19 and the relative rotation between the ratchet 7 and the base plate 5 is restricted, so that the locked state is achieved again.
As illustrated in FIG. 6, between a first level locked state A and a reclined state D, when the operating shaft 12 is operated and the rotation cam 9 is rotated to unlock and the operating force to the operating shaft 12 is released, the pawls 10 are restored to the locked position by the urging force of the spiral spring 19, so that the locked state is achieved.
In contrast, in an unlock retained state C which is between the first level locked state A and a forward folded state B, the projecting portions 10b and 10c of the pawls 10 are positioned in the narrow portion 13d of the cam holes 13b, and even when the operating force to the operating shaft 12 is released, the respective pawls 10 are retained in the unlocked position, so that the seatback 3 may be rotated without operating the operating shaft 12.